The Accomplishments of Muslim Astronomy at a Glance

Astronomy was one of the earliest sciences to thrive in Islam.
In the 8th century, Al-Fazari (d.777) became the
first to construct astrolabes. The astrolabe was a multi
functional instrument that served for nearly ten centuries to
make all sorts of calculations. Al-Fazari also wrote on the
armillary sphere, and the calendar.[1]
Soon after, Mash’allah (d.815) took part with the Persian
al-Naubakht in the preliminary surveying of the foundation of Baghdadin 762-763. HisDe Mercibus, is the oldest scientific work in Arabic,[2]
and was
translated by Gerard of Cremona in the 12th century.[3]

Under Al-Mamun (r. 813-833),
an observatory was completed in 829, a major landmark in the
history of astronomy, from which, in the year 830, the position
of the solar apogee was determined at 82039'.[4]Astronomers at Al-Mamun’s court also
found the inclination of the ecliptic to be 23033’.[5]
Al-Mamun also supervised two geodetic surveys in Iraqfor the purpose of
determining the length of a degree of the meridian, reaching a
result of a degree being equal to 562/3 miles.[6]
The earth’s circumference was found
to be 40,253.4 kms (the accurate figure being 40,068.0 km
through the equator, and 40,000.6 km through the poles.)[7]

One
of the astronomers at the court was Habash al-Hasib (d.864). A
number of works are ascribed to him, and they include the
Mumtahan Zij (The Tested Astronomical Table), The Ma’muni
Zij; on the Rukhamat (Measurements); on the celestial
sphere; on astrolabes; on the Oblique and perpendicular Planes;
and on the Distance of the stars.[8]
He made observations of
solar and lunar eclipses and of planetary positions at
Baghdad
, Samarra
and Damascus
.[9]
He compiled astronomical tables and gave the first instance of
determination of time by altitude,
besides introducing the notion of shadow (umbra versa)
corresponding to our tangent, and compiling a table of tangents,
probably the earliest of its kind.[10]

Also at
the court was al-Khwarizmi (d.863) better known as a
mathematician, on which much will be said further on. He wrote
on the astrolabe, compiled a set of astronomical tables of
future planetary and stellar positions, and also became
one of the first to compute astronomical and trigonometrical
tables.[11]

Al-Farghani (fl. 861) also worked at the same court. His best
known work Kitab fi Harakat Al-Samawiyah wa Jaamai Ilm
al-Nujum (The Book on the Movement of the Planets
, and Compendium of the Science of the Stars) is a manual of
cosmography of thirty chapters. It includes a description of the
inhabited part of the earth, its size, the distances of the
heavenly bodies from the earth and their sizes, and other
matters. Relying on measurements made at the court, Al-Farghani
made many corrections to Ptolemy.[12]
He
published astronomical tables, and wrote about sundials.[13]
He gave the radius of the earth at 3250 miles, and the greatest
distance to the moon as 64 1/6, Mercury 167, Venus 1120, the sun
1220, Mars 8876, Jupiter 14405, and Saturn 20110 earth radii
respectively; gave the apparent diameter of the sun and moon as
31 2/5, and the apparent diameters of the planets at mean
distance as Mercury
1/15, Venus 1/10, Mars 1/20, Jupiter 1/12, and Saturn 1/18 solar
diameters.[14]Amongst Al-Farghani’s other
contributions are his establishment of the Nilometer of Fustat
(old Cairo),
and two unpublished treatises one on the astrolabe, and the
other on the construction of sundials.[15]
Gerard of Cremona translated his Liber 30 differentiarum
also known as Compilatio astronomica;[16]and through much of the centuries
to follow this work
remained much prized through the Latinand Hebrew translations.[17]

Much
of modern astronomy derives from the pioneering studies of
Al-Battani(d.929).
For the major part of his life, Al-Battani worked at
al-Raqqa on the Euphrates. He made
observations from 877 onwards, which ended in the compilation of
a catalogue of stars for the year 880, and the accurate
determination of astronomical coefficients. His
Sabian Tables (al-Zij al-Sabi) had great impact on
his successors, Muslim and Christian, in equal measure.[18]This Zij or collection of astronomical tables with rules
for their use, is one of the very few works of its kind
published in a modern, critical edition.[19]
The arrangement of the 57 chapters in it, unlike Ptolemy’s
Almagest, is dictated by practical rather than theoretical
considerations.[20]
Al Battani starts his Zij with purely practical definitions and
problems: the division of the celestial sphere into signs and
degrees, and prescriptions for multiplication and division of
sexagesimal fractions.[21]
It includes a trigonometrical summary wherein not only sines,
but tangents and cotangents, are regularly used.[22]
It contains a table of cotangents by degrees and a theorem
equivalent to the modern formula giving the cosine of a side of
a spherical triangle as function of the cosine of the opposite
angle and of the sines and cosines of the other sides.[23]
Known in the LatinMiddle Ages as the
De scientia stellarum,
it was influential in select circles in medieval Europe after it
had been translated into Latin by Robert of Chester (lived in Spain 1141-1147). Another version
was by made by Plato of Tivoli (lived in
Barcelona
about 1134-1145) at about the same time.[24]
It impacted most particularly on Abraham Ibn Ezra, Richard of
Wallingford; Levi Ben Gerson; Regiomontanus; Peurbach; and
Copernicus.[25]

Al-Battani’s
other accomplishments were many. Amongst others, he determined
the longitude of the sun’s apogee at 830 15’; he also
gave the greatest distance of the moon as 641/6, Mercury 166,
Venus 1070, the sun 1146, Mars 8022, Jupiter 12924, and Saturn
18094 earth radii respectively.[26]Al-Battani also discovered
the motion of the solar apsides,[27]
besides working on the timing of the new moons, the
length of the solar and sideral year, the prediction of
eclipses, and the phenomenon of parallax, carrying us according
to Wickens ‘to the verge of relativity and the space age.'[28]
Al-Battanifixed
precisely the ‘Obliquity of the Ecliptic’ i.e the inclination of
the celestial equator with reference to the Zodiacs at 230
35’.[29]Al-Battani's observations of eclipses
made in the 10th century were still used as late as
1749 for comparative purposes.[30]
His improved tables of the sun and the moon helped him
discover that the direction of the sun's eccentric as recorded
by Ptolemy was changing, which means that the earth is moving in
a varying ellipse.[31]
Al-Battani was sceptical of Ptolemy's practical results, and
relying on his own observations, he corrected Ptolemy's errors.[32]
The corrections cover the main parameters of planetary motion no
less than erroneous conclusions drawn from insufficient or
faulty observations, such as the invariability of the obliquity
of the ecliptic or of the solar apogee.[33]
According to Al Battani:

‘After having lengthily applied myself in the study of this
science (astronomy), I have noticed that the works on the
movements of the planets differed consistently with each other,
and that many authors made errors in the manner of undertaking
their observation, and establishing their rules. I also noticed
that with time, the position of the planets changed according to
recent and older observations; changes caused by the obliquity
of the ecliptic, affecting the calculation of the years and that
of eclipses. Continuous focus on these things drove me to
perfect and confirm such a science.’[34]

After he had completed pinpointing and demonstrating diverse
astronomical operations, which he supported bymathematical calculations, Al-Battanisummoned others after
himself: ‘to continue observation, and to search,’ saying that
it was no impossibility that with the passing of time, more
could be found, just as he himself had added to his
predecessors. ‘Such is the majesty of celestial science, so
vast, that none could ever encompass its study by himself.’[35]

One
of the major contributions of al-Battani to the science was his
use of the widest variety of instruments. He used an astrolabe
in connection with a problem which did not require a very exact
measurement.[36]
There occurs a gnomon for careful observations which was divided
into twelve parts but was capable of divisions into smaller
fractions.[37]
He had sun clocks both horizontal and vertical.[38]
He had an armillary sphere, whose dimensions are not mentioned.[39]
He used parallactic rulers whose dimensions are not known with
certainty, but he recommends the use of one whose measurements
are equivalent to those performed on a circle of about five
meters diameter.[40]
He had a mural quadrant; for this instrument he recommends a
radius of not less than one meter, and adds that the larger the
dimension the more exact it becomes.[41]
His opting for the largest instruments is evident, and the
measures taken by the parallax rules relate to a circle of no
less than five meters in diameter; and the quadrant was no less
than one meter.[42]
Speaking of measurements of the obliquity of the ecliptic, he
says:

‘We
have observed it in this time of ours with the parallactic ruler
and the mural quadrant…. After having made their divisions very
precise and securing them in their place as carefully as
possible.’[43]

The
impact of Al-Battanion Western Christian
science is considerable. Copernicus’ indebtedness to him is
widely known, as he quotes him fairly often, just as does
Peurbach in the chapters dealing with the subjects of solar
motion and of precession; and so did Tycho Brahe, Kepler and
Galileo, who all showed interest in his observations.[44]
And whilst Regiomontanus valued very highly Al-Battani’s spheric
trigonometry, Denton profited much from
his observation of the eclipses as late as 1749.[45]Such was the impact of Al-Battani on the science, Lalande
considered him one of the twenty most important scholars that
ever lived.[46]

Around the same time as Al-Battani
, there flourished three astronomers of great accomplishment:
Al-Sufi, Ibn Yunus, and Al-Biruni
. Al-Sufi’s (903-986) contribution is wide ranging, including
critical revisions of Ptolemy; writing on the astrolabe (more on
which further on), as well as observations on the obliquity of
the ecliptic and the motion of the sun (or the length of the
solar year.)[47]
He was better known for his observations and descriptions of the
stars, though. He set out his results constellation by
constellation, discussing the stars, their positions, their
magnitudes (brightness) and their colour, and for each
constellation, providing two drawings, one from the outside of a
celestial globe, and the other from the inside (as seen from the
sky).[48]
Al-Sufi was the first to critically revise the star catalogue of
Ptolemy, adding the differing or additional results of his own
observations which are embodied in his compendium: Kitab
suwar al-Kawakib al-Thabita (On the Constellations of the
Fixed Stars).[49]
The work has the exact identifications of several hundred of the
old Arabic star names, and it is fairly appropriate to mention
here that the Muslims named many of the stars and constellations
(several of which are still with us: Aldeberan, Altair and
Betelgeuse, for instance), and devised such good star maps that
they were used in both Europe and the Far East for centuries to
come.[50]
(To glean more on this subject of stars, there is no better
authority than Kunitzsch.)[51]
Al-Sufi also wrote a book on the use of the celestial globe, and
he constructed astronomical instruments as well. A silver
celestial globe manufactured by him is said to have been extant
in Egyptaround 1043.[52]

Ibn Yunus (d. 1009), from Egypt
, is better known for his Hakemite tables, which he devised
after nearly thirty years (977-1003) of observation. He, too,
maintained the tradition of using a wide variety of instruments,
including a large astrolabe of nearly 1.4 m in diameter. His
tables contain more than 10,000 entries of the sun's position
throughout the years.[53]

Al Biruni’s (973-1050) contribution to science is vast, and his
name will keep on re-appearing. He wrote a total of 150 works on
all the sciences of his time, including 35 treatises on pure
astronomy, of which only six have survived.[54]
One of his early claims was that the earth rotated around its
own axis.[55]
He also calculated the earth’s circumference, and there is an
exceptionally good account by Baloch on his experiment at
Nandana (India
) to measure the earth’s circumference.[56]
Al-Birunialso fixed
scientifically the direction of Makkahfrom any point of the
globe.[57]

Unlike what is generally asserted by mainstream historians, the
overwhelming majority of Muslim scholars, whether east or west,
condemned astrology.[58]
Al-Biruni,
just named, spent a great deal of time in serious study of the
subject,[59]
his astrological sections of Al-Qanun al-Masudi (The
Masudi Canon) warning against belief in astrology.[60]
He goes so far as to say that he discussed astrology in detail
in order to warn the intelligent man away from it.[61]
Krause has collected passages in which al-Biruni not only heaps
ridicule upon ignorant or unscrupulous astrological
practitioners, but indicates disbelief in the basic tenets of
this pseudo science.[62]
Al-Biruni's book that would have elaborated his attack against
astrology is only known by name, its title, Warning Against
the Craft of Deceit, meaning astrology, leaving very little
doubt as to Al-Biruni’s position on the matter.[63]

A great number of other Muslim astronomers and scholars warned
against astrology. Al-Farabi (d. 948) is one of them.[64]
Ibn Sinadwells upon the
falseness of the doctrines and assumptions upon which astrology
is based, and he speaks of the credulity of people with regard
to their belief in astrology and similar pseudo sciences.[65]
In their defence, for making errors in their predictions,
astrologers held that physicians, too, made errors,[66]
to which Ibn Sina responded that this analogy was without basis,
and that in contrast to medicine, astrology lacks any scientific
foundation.[67]
According to Fakhr Eddin al-Razi (d. 1209) Abu Sahl al-Masihi,
teacher of Ibn Sina, was against astrology and had written a
special treatise refuting it.[68]
Fakhr Eddin himself was antagonistic to it.[69]
Ibn Khaldunalso attacked astrology
on the ground that it had no utility and that it causes
spiritual and material injury to humans.[70]
The stance against astrology in Islam follows a long tradition
from the time of the Prophet who said:

‘Those who say the rain that we receive comes from the kindness
of God and from His mercy believe in me and do not believe in
the stars but those who say the rain that we receive comes from
the star do not believe me but believe in the stars.’[71]

In Muslim Spain, astronomers pursued the tradition of the Muslim
East, and wrote on a diversity of matters, giving a prominent
place to instruments, and once more, mounting anonslaught on Ptolemy’s astronomy.
Maslama (al-Majriti) (d.1007) wrote ‘some chapters indispensable
for everyone who wishes to construct an astrolabe,'.[72]
He also edited and adapted Al-Khwarizmi’s
tables to places in
Spain.

Al-Zarqali (1029-1087) wrote two treatises on instruments,
devised the Toledan Tables for the year 1080; and amended
Ptolemy's exaggerated estimate of the length of the
Mediterraneansea from 620
to nearer to its correct value of 420.[73]
Al-Zarqali is said to have found the movement of the solar
apogee, which he held to be 1degree in 299 years, on the basis
of twenty five years of observation.[74]
The motion of the solar apogee with reference to the
stars, he said, amounted to 12.04'' a year. He also gave a value
of 770 50' for the longitude of the sun's apogee, and
concluded that the inclination of the ecliptic oscillated
between 23033' and 23053'.[75]
Al-Zarqali’s Tratado de la lamina de los siete planetas
is a predecessor to the Aequatorium planetarium of the
Renaissance, and its Arabic text contains the clarification of
one of the most debated passages of medieval astronomy.[76]
In the graphic representation included in the Castilian
translation ordered by Alfonso the Wise, the orbit of mercury is
not circular.[77]
On this basis, Al-Zarqali might have anticipated Kepler in
stating that orbits (the orbit of Mercury in this case) are
elliptical. Al-Zarqali treated Mercury in the same deductive way
that Kepler dealt with Mars in his Astronomia Nova.[78]
The conclusion by Hartner is that ‘it is not known whether
Kepler knew of al-Zarqali’s text,’[79]
which is somehow unfair on the Muslim scholar, for whilst Muslim
scholars and scholarship are condemned for their borrowing from
the Greeks, however faint the resemblance between the two, when
it comes to later Western scientific findings, the same
principle of resemblance is never applied, even when such
resemblance between the Islamic and the Western is very obvious.

Jabir Ibn Aflah (d. 1150) is specially noted for his work on
spherical trigonometry,[80]a
real step forward, including, for instance, a new method of
solving a right angled spherical triangle.[81]
Jabir has alsobeen credited
with the invention of the turquet,[82]
and other instruments. He devoted
great effort to amend Ptolemy’s theory of the planets.
Lorch has examined this issue in detail.[83]
In the section on the sphericity of the heavens, Jabir describes
Ptolemy’s reasoning as, ‘extremely compact and abbreviated-hence
the worthlessness of the reasoning.’[84]

The
most famous of Jabir’s criticisms concerns the position of Venus
and Mercury. Ptolemy placed them between the Moon and the Sun,
which thus divided the planets of limited elongation from those
which could have any elongation. They have never eclipsed the
Sun because they have never been in line with it-just as most
conjunctions of Sun and Moon produce no eclipse. The question
cannot be settled, Ptolemy says, because Venus and Mercury show
no parallax, from which their distance from Earth could be
measured, and placing them nearer the Sun would not entail any
parallax even at their perigees.[85]
Jabir begins:

‘I
am very puzzled by what kind of man this is. I am quite at a
loss to account for this inconsistency and confusion of his,
which he did not notice. Such a thing must be very alien to
anyone who makes any considerable study of these things, as he
did. He did not see his inconsistency.’
[86]

Jabir then points out that Ptolemy himself had reckoned a
maximum solar parallax at 2’51’’, and that if Venus and Mercury
were within the Sun’s sphere, Venus would have a parallax of
about a third of degree (the figure is almost exactly 19’,
actually) at its perigee and Mercury 7’. Jabir reasons that
Venus’ apogee must at best be the same distance from the Earth
as the Sun’s perigee, and scales up the parallax accordingly, a
procedure that is accurate enough for such small angles. He is
evidently considering Mercury as fitting beneath the Sun
separately, for if he had calculated for both planets’ being
beneath the Sun (when Mercury’s apogee is the same distance from
the Earth as Venus’ perigee), then Mercury’s maximum parallax
becomes just over 47’. Jabir considers it possible that the
parallaxes he has calculated have not been observed, since to
show them the planets would have to be in conjunction with the
Sun. So he calculates the parallaxes for maximum elongation, 6’
for Venus and 4’ for Mercury (actually, 7’ and 4½’ are better
figures).[87]
The argument is brought to a triumphant climax:

‘Since, therefore, no parallax worth bothering about (according
to Ptolemy) is to be found in either of them, and the Sun does
have a sensible parallax worth bothering about, how can they be
below the Sun.?’[88]

Al-Bitruji (d. c 1204), too, modified Ptolemy’s system of
planetary motions; but unlike Jabir, in his planetary theory, he
positioned the Sun between Venus and Mercury.[89]
Al-Bitruji’s Kitab al-Haya, is, according to Hetherington
(who relies on MacKenzie and Sarton in his summing up):

‘An
attempt to revive in a modified form the theory of homocentric
spheres: each heavenly body is attached to a sphere and the
motive power is the ninth sphere outside the fixed stars. The
prime mover produces in every sphere a motion from east to west;
this motion is faster in the eighth sphere, and it decreases as
the distance from the prime mover increases, e.g., the fixed
stars complete a revolution in 24 hours, while the moon, which
is carried by the innermost sphere, requires almost 25 hours for
the same revolution. The pole of the ecliptic being different
from that of the equator, the planetary orbits are not closed;
moreover, the planets do not remain at an invariable distance
from the pole of the ecliptic; each has its own motion in
latitude, and a variable velocity in longitude. The eighth
sphere has two motions, the one in longitude (precession), and
another caused by the rotation of the pole of the ecliptic
around a mean position (this is the imaginary trepidation of the
equinoxes). The pole of each planet revolves around the pole of
the ecliptic, each in its own way. His theory was called the
theory of spiral motion.’[90]

Kitab-al-Hay’ah’
was translated by the Sicilian based Michael Scot under the
title ‘On the Sphere.' Its impact was strongly felt thereafter,
the
first author to be widely influenced being William of Auvergne,
who endorses his system in his encyclopaedic work De Universo.[91]

Muslims compiled a great numbers of zijs, that is astronomical
handbooks with text and tables; in 1956, E.S. Kennedy publishing
a survey of 125 such Islamic Zij;[92]
a number that has risen to close to 200, authored by names such
as Al-Khwarizmi,
al-Battani, al-Biruni, Ibn al-Banna (Marrakechfl. 1300).[93]Most Zij consist of several hundred pages of text and
tables; the treatment of the material presented varying from one
zij to another, but most contain chapters and tables relating to
the following aspects of mathematical astronomy:

Mathematical astronomy is concerned with the determination of
the position of the sun, the moon, planets and fixed stars; the
prediction of planetary conjunctions, eclipses, visibility of
lunar crescent, time keeping by the sun and the stars etc. King
informs us that the science has a long Yemeni tradition, from
the 10th century until the present; with about one
hundred manuscripts dating from the medieval period that have
survived.[95]
Like the rest of Muslim works in other sciences, they can be
found scattered in libraries across the world. The Yemeni works
on astronomy are very precious not just in their own right, but
also because they include material from sources since lost. Each
year, almanacs and ephemerids were prepared for the Yemeni
sultans by their astronomers that included tables of the
position of the sun, moon, and planets for each day of the year.
Two manuscripts on these subjects survive. The first Yemeni
astronomer about whom there is reliable information is
Al-Hamdani, who compiled a Zij. The second, Abu’l-Uqul worked
for Sultan al-Mu’ayyad, and compiled a Zij based on the works of
Ibn Yunus, which can no longer be found; this Yemeni work
salvaging what would otherwise have been lost.[96]
Abu’l-Uqul’s contribution was also to prepare tables for
time-keeping by the Sun and the stars for the latitude of Ta’iz;
a corpus that is the largest known for any medieval Islamic
city, containing over one hundred thousand entries.[97]
Yemeni rulers had their contributions, too, including Sultan
al-Muzaffar, who sponsored two astronomers, al-Farisi and
al-Kawashi. The first prepared a Zij containing tables for the
Yemen,
whilst the second prepared a Zij with tables specifically for
Aden and Ta’izz. Sultan al-Ashraf, for his part, compiled a
treatise on the construction of astrolabes and sundials, and
also prepared new tables of coordinates for drawing the curves
on astrolabe plates and the curves on horizontal sundials,
computing these tables for the latitudes of the major centres of
the Yemen and the Hijaz.[98]
One of the astrolabes made by al-Ashraf is now at the
Metropolitan Museum of Art in New York; but more crucially, as
noted by King, al-Ashraf’s treatise contains in the appendix a
discussion on the magnetic compass.[99]
Like al-Ashraf, Sultan al-Afdal compiled an extensive compendium
of astronomical treatises and tables, derived from various
sources, now lost. And so were the works of the early Yemeni
astronomers, with the exception of those few that survive
scattered in the libraries of the world.

Whether east or west of the Islamic land, the mid-late 13th
century brought a sharp decline in astronomical writing. In the
West this followed the loss of Muslim Spain; in the East, this
was due to the crusader-Mongol onslaught. The activity of worth
east of Egyptwas represented by the
Maragha observatory, whose erection was due not to Mongol
scientific investigation, but rather to their leader Hulagu’s
reliance on the stars for the conduct of his wars against the
Muslims.[100]
At his service was the astrologer Nasir Eddin Al-Tusi (b.1201),
who advised him on the onslaught against Baghdadin 1258.[101]
There, subsequently, nearly a million lives were wiped out.[102]
Al-Tusi was put in charge of the said observatory, which enabled
him to prepare the Il-Khani Tables, a catalogue of fixed stars,
and prepare a treatise on the Quadrilateral,[103]
a work on spherical trigonometry.[104]
In the same environment Ibn al-Shatir, al-Urdi, and Muhi Eddin
al-Maghribi also worked. Al
Urdi (d. 1266) of Aleppowas the first to
initiate the construction of planetary models, besides
constructing other instruments, detailed in his The Instrumentsof the Observatoryof Maragha.[105]
Ibn al-Shatir is widely held to have been at the source of the
planetary theory devised centuries later by Copernicus.[106]

In
the final decades of the 13th century, Mamluk Egypthad probably the best
contribution to astronomy of this later period. Amongst its
astronomers was Al-Marrakushi, who was of Moroccan origin but
who worked in Cairo. He
wrote Kitab al-mabadi wa’l ghayat fi ilm al-Miqat (A
Compendium of Astronomical Time Keeping), a complete survey of
spherical astronomy and astronomical instruments.[107]
Shihab Eddin al-Maqsi, who flourished in Cairo, compiled a
treatise on sundial theory, and a set of tables for
time-keeping.[108]
Najm Eddin al-Misri, also flourished in Cairo, and compiled a
table for time keeping that could be used not only for all
latitudes but also for time keeping by the Sun by day and by the
stars by night.[109]

After the 13th century, just as with every other
science, astronomical output dwindled considerably. Al-Kashi and
his fellow members of the Samarqand observatory, to be
considered further on, being the authors of a final flowering of
Islamic astronomy (and mathematics). Other later figures include
Ibn
Qunfudh (d.1407), an Algerian historian, mathematician and
astronomer, who wrote ‘Help to the Students for the
Determination of the Positions of the Planets.’[110]
In 1475, Al-Suyuti of Cairocompiled a treatise on
the references to astronomy in the Qur’an.[111]
In 1480, Cyriacus wrote a zij entitled Durr al-Muntakhab
(The Chosen Pearl), calculated for the city of Mardin in
south-east modern Turkey; with one set of planetary tables,
about 10,000 values for each planet, and instructions on how to
determine the position of any planet at any time using only
addition.[112]
The Moroccan astronomer al-Rudani
(1623-83) was probably the last Islamic astronomer of any worth.
He invented a spherical engine, which functioned within shells,
that was used to measure time, and that could be operated at any
longitude or latitude.[113]